Method and system for coating a medical device using optical drop volume verification

Abstract

A method and apparatus for controlling coating material deposition on to a medical device. Images of material drops in flight are captured and an average single drop volume value is calculated by conversion of the captured drop images to a volume measurement. The average single drop volume value is used to calculate a total number of drops necessary to apply a desired amount of coating. Alternately, material is applied and the amount of material deposited is accumulated and adjustments are made to deposit only a desired amount of coating material. A drop volume is determined for either every drop or a sampling of drops as the drops are being applied. Adjustments to the coating process include changing drop size and changing a number of drops to be deposited.

1. A system for applying droplets of coating material onto a medical device, the system comprising:
 a support for a medical device to be coated, the support being movable relative to a first axis; 
 an applicator, the applicator being movable relative to a second axis, the second axis being parallel to the first axis, the applicator configured to emit droplets of coating material, each droplet having a droplet path between the applicator and the support; 
 a strobe light, the strobe light being coupled to the applicator, the strobe light synchronized with the applicator so that the strobe light illuminates at least one droplet of coating material on the droplet path after the at least one droplet has been emitted from the applicator; 
 an imaging system, the imaging system being substantially perpendicular to the droplet path, the imaging system configured to capture an image of the at least one droplet that has been illuminated by the strobe light, the at least one droplet being positioned on the droplet path; 
 an image processing system, the image processing system configured to analyze an image obtained by the imaging system; 
 a control system, the control system in communication with the applicator, the support, and the imaging system; 
 a user interface, the user interface in communication with the control system; and 
 a blocker in communication with the control system, wherein the blocker is configured to capture an entirety of at least one droplet of coating material after the at least one droplet has been emitted from the applicator during one or more calibration phases of the system for confirmation that droplets of a desired drop volume are being emitted from the applicator, the blocker being positioned in the droplet path. 
 
     
     
       2. The system of  claim 1 , wherein the applicator is a drop on demand applicator. 
     
     
       3. The system of  claim 1 , wherein the support is rotatable about and movable along the first axis. 
     
     
       4. The system of  claim 1 , the system further comprising a medical device on the support. 
     
     
       5. The system of  claim 4 , wherein the support is either a mandrel or a balloon catheter. 
     
     
       6. The system of  claim 1 , wherein the image processing system comprises a part of the control system. 
     
     
       7. The system of  claim 1 , wherein the image processing system is configured to determine a drop volume of a single droplet with a program, wherein the program includes instructions for slicing analysis wherein the slicing analysis comprises:
 dividing the image of the droplet into a number of slices from a first end of the image of the single drop to a second end of the image of the single droplet; 
 determining the volume of each slice of the number of slices; and 
 adding the volumes of each of the number of slices to obtain an in-flight volume of the single droplet. 
 
     
     
       8. The system of  claim 1 , wherein the image processing system is configured to determine an average drop volume of a plurality of sequential droplets from an image of the plurality of sequential droplets with a program, wherein the program includes instructions for an edge detection technique, wherein the edge detection technique comprises:
 determining an average drop image of the image of the plurality of sequential droplets; 
 determining an outline of the average drop image; and 
 determining the average drop volume from the outline of the average drop image. 
 
     
     
       9. The system of  claim 8 , the image of the plurality of sequential droplets being captured by the imaging system during an exposure time wherein the strobe light flashes a plurality of times during the exposure time and each strobe light flash illuminates a different drop of the plurality of sequential droplets. 
     
     
       10. The system of  claim 1 , wherein the control system has programming with instructions to perform at least one task selected from the group consisting of:
 directing the applicator to emit a droplet of coating material according to user selectable attributes provided to the control system; 
 positioning the applicator relative to a medical device being coated; 
 positioning the support relative to the applicator; 
 adjusting a size of droplets of coating material being emitted by the applicator; 
 adjusting a number of droplets of coating material to be emitted by the applicator from an initial number of droplets; 
 and any combination thereof. 
 
     
     
       11. The system of  claim 10 , wherein adjusting the size of droplets and adjusting the number of droplets each depend on a measured volume of the at least one droplet. 
     
     
       12. The system of  claim 1 , wherein the user interface allows a user to input user selectable attributes for the system, user selectable attributes being at least one of material type, drop size, drop velocity, total volume of coating material to deposit, and temperature. 
     
     
       13. The system of  claim 12 , wherein the user interface forms a part of the control system. 
     
     
       14. The system of  claim 1 , wherein the blocker:
 is made of a material configured to absorb the at least one droplet of coating material; or 
 includes a reservoir or spittoon; or 
 includes a suction or vacuum system. 
 
     
     
       15. A system for applying droplets of coating material onto a medical device, the system comprising:
 a support for a medical device to be coated, the support being movable on a first axis; 
 an applicator movable on a second axis parallel to the first axis, the applicator configured to emit droplets of coating material; 
 a strobe light coupled to the applicator, the strobe light synchronized with the applicator so that the strobe light illuminates at least one droplet of coating material in flight after the at least one droplet has been emitted from the applicator; 
 an imaging system substantially perpendicular to a droplet in flight, the imaging system configured to capture an image of the at least one droplet in flight that has been illuminated by the strobe light; 
 an image processing system, the image processing system configured to analyze an image obtained by the imaging system; 
 a control system, the control system in communication with the applicator, the support, and the imaging system; 
 a user interface, the user interface in communication with the control system; and 
 a blocker in communication with the control system, wherein the blocker is configured to capture an entirety of at least one droplet of coating material emitted from the applicator during one or more calibration phases of the system, wherein the blocker:
 includes a reservoir or spittoon; or 
 includes a suction or vacuum system 
 
 the system having;
 a coating configuration, wherein the applicator is configured to emit the droplets of coating material toward the support for coating the medical device; and 
 a calibration configuration in the one or more calibration phases, wherein the applicator is configured to emit the droplets of coating material toward the blocker for confirmation that droplets of a desired drop volume are being emitted from the applicator. 
 
 
     
     
       16. The system of  claim 15 , wherein the blocker is positioned between the applicator and the support only in the calibration configuration; and
 further wherein the strobe light is configured to illuminate the at least one droplet of coating material in flight when the system is in the coating configuration and when the system is in the calibration configuration. 
 
     
     
       17. The system of  claim 15 , the applicator having a coating position when the system is in the coating configuration and a calibration position when the system is in the calibration configuration, the calibration position being different from the coating position, wherein the applicator is configured to pivot from the coating position to the calibration position and from the calibration position to the coating position;
 wherein the strobe light is configured to illuminate the at least one droplet of coating material in flight only when the system is in the calibration configuration. 
 
     
     
       18. The system of  claim 15 , wherein the image processing system is configured to determine a drop volume from the image with a program, wherein the image is either:
 a) an image of a single droplet, wherein the drop volume is a drop volume of the single droplet and the program to determine the drop volume of the single droplet includes instructions for a slicing analysis, wherein the slicing analysis comprises:
 dividing the image of the droplet into a number of slices from a first end of the image of the single drop to a second end of the image of the single droplet; 
 determining the volume of each slice of the number of slices; and 
 adding the volumes of each of the number of slices to obtain an in-flight volume of the single droplet; or 
 
 b) an image of a plurality of sequential droplets, wherein the drop volume is an average drop volume of the plurality of sequential droplets, wherein the program to determine the average drop volume of the plurality of sequential droplets includes instructions for an edge detection technique, wherein the edge detection technique comprises:
 determining an average drop image of the image of the plurality of sequential droplets; 
 determining an outline of the average drop image; and 
 determining the average drop volume from the outline of the average drop image.